1. Field of the Invention
This invention relates to new and useful improvements in drag blade bits and more particularly to drag blade bits having diamond cutters along the cutting edges thereof.
2. Description of the Prior Art
Drilling tools or bits for drilling holes in the ground have been known since prehistoric times. There is evidence, as far back as 30,000 years ago, of the use of wooden drills for working in stone and shells. Tools for digging wells, such as picks, bars, shovels, etc. have been in use since antiquity. The earliest mechanically operated percussion drills were used by the Chinese about a thousand years ago. Rotary drilling tools for boring holes were used in stone quarries of Egypt from the time of the construction of the Pyramids.
The development of drill bits for oil well drilling dates from the 1860s. Von Ringharz U.S. Pat. No. 228,780 discloses a rotary drag bit used in drilling artesian and other wells. That patent also describes the use of the circulation of water through a drill string for flushing cuttings from the bore hole.
Rotary blade bits, and particularly fish tail bits, were used extensively during the early days of oil well drilling. Rotary blade type drag bits were used primarily for drilling through shale and other soft formations. The rotary blade bits were also useful in clay and gumbo type formations. These bits were capable of drilling at a fairly high speed but would wear out in a relatively short distance. It was not unusual for a rotary drag bit to wear out in 75' to 100' of drilling. Also, whenever harder formations were encountered, the drag bits would not drill satisfactorily.
In the History of Oil Well Drilling, J. E. Brantly, Gulf Publishing Company, 1971, Chapter 21 "Rotary Bits" describes in detail the history of development of drill bits for oil well drilling. Numerous examples are given of the early drag bits which were used for shallow wells and particularly for drilling through soft formations. The rotary drag bits or blade bits were largely replaced in later years by roller cone bits and other bits capable of drilling through harder, rock formations. The rotary blade bits, however, have continued in use to the present day and are used still for drilling through shale and other soft formations.
Because of the fact that rotary blade bits wear out rapidly in use, there were numerous attempts made to increase the wear life of those bits. As early as 1923, tungsten carbide was used as a diamond substitute in core drilling. The high expense of tungsten carbide restricted its use to core bits until cheaper methods of manufacture were discovered. As a cheaper tungsten carbide became available, it was used in hard facing of rotary bits. Tungsten carbide hard facing was used on rotary blade bits and other drag bits and later was used on the gage surfaces of roller cone bits. In addition, tungsten carbide was used first in coating the teeth of milled tooth bits and later in the manufacture of hard inserts for roller bits.
The development of hard facing for drag blade bits extended the life of the bits somewhat but not enough to overcome the need for frequent replacement. Rotary blade bits are customarily used until worn out and then removed from the bore hole. The blades can be cut off from the bit body by a welding torch and a new blade welded in place. This has allowed the bits to be reused but has not overcome the problem of expensive down time for replacing a worn out bit.
In the patent literature:
Pace U.S. Pat. No. 1,351,003 discloses a blade type drag bit having replaceable blades. PA0 Olsen U.S. Pat. No. 2,855,181 discloses a drag bit with stepped cutting edges and hard facing on certain of the wear surfaces. PA0 Weaver U.S. Pat. No. 2,894,726 discloses another drag blade bit having wear inserts. PA0 Christensen U.S. Pat. No. 3,106,973 discloses rotary blade bits having replaceable blades with fine diamond particles embedded in the cutting surfaces. PA0 Bridwell U.S. Pat. No. 3,127,945 discloses a drag blade bit having blades of conventional design provided with diamonds embedded in the cutting and wear surfaces.
The application of finally divided diamonds in wear surfaces of drag bits has been expensive and difficult.
In recent years, there has been developed an improved type of diamond cutter which utilizes synthetic diamonds.
Rowley U.S. Pat. No. 4,073,354 and Rohde U.S. Pat. No. 4,098,363 discloses diamond cutting bits of advanced design. An example of cutting inserts using polycrystalline diamond cutters and an illustration of a drill bit using such cutters is found in Daniels U.S. Pat. No. 4,156,329 and Dennis U.S. Pat. No. 4,323,130.
The most comprehensive treatment of this subject in the literature is probably the chapter entitled STRATAPAX Bits, pages 541-591 in ADVANCED DRILLING TECHNIQUES by William C. Maurer, the Petroleum Publishing Company 1421 South Sheridan Road, P.O. Box 1260, Tulsa, Okla. 74101, published in 1980. This reference illustrates and discusses in detail the development of the STRATAPAX diamond cutting elements by General Electric and gives several examples of commercial drill bits and prototype using such cutting elements. A substantial number of patents and publications have been issued since the publication date of ADVANCED DRILLING TECHNIQUES and so an up-to-date consideration of the prior art must include the recently issued patents.
While the prior art discloses a variety of diamond bits utilizing the STRATAPAX or equivalent diamond cutting elements, this type of diamond cutting element does not seem to have been utilized in producing drag blade bits having extended wear life.